The temperature of a certain cup of coffee 10 minutes after

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The temperature of a certain cup of coffee 10 minutes after [#permalink]

28 Jul 2010, 09:11

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The temperature of a certain cup of coffee 10 minutes after it was poured was 120 degree Fahrenheit . If the temp F of the coffee t minutes after it was poured can be determine by the formula F=120 (2^-at)+60 , where F is degree Fahrenheit and a is constant, then the temperature of the coffee 30 minutes after it was poured was how many degree Fahrenheit

A. 65
B. 75
C. 80
D. 85
E. 90

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Re: Problme [#permalink]

28 Jul 2010, 11:57

Hi,

Since F=120 (2^-at)+60,
replace F=120, t=10 to find a.
Once you find a, then to find the temperature 30 min after it was poured simply replace
t=30 and value of a in the equation.

regards,
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Re: Problme [#permalink]

28 Jul 2010, 13:26

Is the question correctly written?? I am unable to find the solution.

F= 120* (\frac{1}{2^at}) + 60
Is this formula correct?
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Re: Problme [#permalink]

28 Jul 2010, 13:40

Yes this is how it is written.

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Re: Problme [#permalink]

29 Jul 2010, 04:03

kilukilam wrote:

The tempreature of a certain cup of coffee 10 minutes after it was poured was 120 degree Faranite. If the temp F of the coffee t minues after it was poured can be determinde by the formula F=120 (2^-at)+60 , where F is degree Fahrenhite and a is constant, then the tempreature of the cofffee 30 minues after it was poured was how many degree fahrenhite

a. 65
b. 75
c. 80
d. 85
e. 90

We have the formula for calculating temperature: F=120*2^{-at}+60 and the value for t=10 --> F(t=10)=120=120*2^{-10a}+60 --> \frac{1}{2^{10a}}=\frac{1}{2} --> 10a=1 --> a=0.1. So formula is F=120*2^{-0.1t}+60

Now for t=30 the temperature in Fahrenheits will be F=120*2^{-0.1*30}+60=\frac{120}{2^3}+60=75.

Answer: B.
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Re: Problme [#permalink] 29 Jul 2010, 04:03

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The temperature of a certain cup of coffee 10 minutes after

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The temperature of a certain cup of coffee 10 minutes after

The temperature of a certain cup of coffee 10 minutes after

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